The modernization increased their armor, replaced and upgraded their machinery, and rebuilt their superstructures into a distinctive pagoda mast style.

[1] The IJN's fleet of battleships had proven highly successful in 1905, the last year of the Russo-Japanese War, which culminated in the destruction of the Russian Second and Third Pacific Squadrons at the Battle of Tsushima.

[2] In the aftermath of that war, the Japanese Empire immediately turned its focus to the two remaining rivals for imperial dominance in the Pacific Ocean: Britain and the United States.

[1] Satō Tetsutarō, a Japanese Navy admiral and military theorist, speculated that conflict would inevitably arise between Japan and at least one of its two main rivals.

Displacing 17,900 long tons (18,200 t) and armed with ten 12-inch (30.5 cm) guns, Dreadnought rendered all existing battleships obsolete by comparison.

[8] When the two new Satsuma-class battleships and two Tsukuba-class armored cruisers, launched by 1911, were outclassed by their British counterparts, the Eight-Eight Fleet Program was restarted.

The Diet amended this by authorizing the construction of four battlecruisers (the Kongō class) and one battleship, later named Fusō, in what became the Naval Emergency Expansion bill.

[12] In an effort to outmatch the American New York class, planners called for a ship armed with twelve 14-inch (36 cm) guns and faster than the 21 knots (39 km/h; 24 mph) of their rivals.

[14][Note 1] The final design—designated A-64 by the IJN—called for a displacement of 29,000 long tons (29,465 t) with twelve 14-inch (36 cm) guns in six double turrets (two forward, two aft, two separated amidships) with a top speed of 23 knots (43 km/h; 26 mph).

The turbines were designed to produce a total of 40,000 shaft horsepower (30,000 kW), using steam provided by 24 Miyahara-type water-tube boilers, each of which consumed a mixture of coal and oil.

[19] The twelve 45-calibre 14-inch guns[13] of the Fusō class were mounted in six twin-gun turrets, numbered from front to rear, each of which weighed 615 long tons (625 t).

[23] Mounted amidships along the centerline of the ship, they had restricted arcs of fire,[13] and their position forced the boiler rooms to be placed in less than ideal locations.

[15] Another complication was the need to fit extra insulation and air conditioning in the magazines of the amidships turrets to protect them from the heat generated in the adjacent boiler rooms.

[21] As built, the Fusō class was fitted with a secondary armament of sixteen 50-caliber six-inch guns mounted in single casemates along the sides of the hull at the level of the upper deck.

This model was the standard Japanese light anti-aircraft gun during World War II, but it suffered from severe design shortcomings that rendered it a largely ineffective weapon.

Additionally, the vessels contained 737 watertight compartments (574 underneath the armor deck, 163 above) to preserve buoyancy in the event of battle damage.

During Fusō's first modernization, four directors for the 12.7 cm AA guns were added, one on each side of the fore and aft superstructures, and an eight-meter rangefinder was installed at the top of the pagoda mast.

[37][Note 2] While the ships were in drydock in July 1943, Type 21 air search radar was installed on the roof of the 10-meter rangefinder at the top of the pagoda mast.

She outclassed her American counterparts of the New York class in firepower and speed, and was considered the "most powerfully armed battleship in the world".

[43] The ship did not take part in any combat during World War I, as there were no longer any forces of the Central Powers in Asia by the time she was completed.

[46] In April and May 1941, Fusō and Yamashiro were attached to the 2nd Division of the 1st Fleet,[47] but the two ships spent most of the war around Japan, mostly at the anchorage at Hashirajima in Hiroshima Bay.

[31] When the war started for Japan on 8 December,[Note 4] the division sortied from Hashirajima to the Bonin Islands as distant support for the 1st Air Fleet attacking Pearl Harbor, and returned six days later.

[46] Commanded by Vice-Admiral Shirō Takasu, the division set sail with the Aleutian Support Group on 28 May, at the same time that most of the Imperial Fleet began an attack on Midway Island (Operation MI).

[31] In July 1943, Yamashiro was at the Yokosuka drydock, then was briefly assigned as a training ship on 15 September before loading troops on 13 October bound for Truk Naval Base, arriving on the 20th.

Shigenori Kami, chief of operations of the Navy Staff, volunteered to command Yamashiro to carry troops and equipment to Saipan.

[52] Fusō was assigned to the Imperial Japanese Naval Academy at Etajima, Hiroshima, for use as a training ship between 15 November 1942 and 15 January 1943.

[31][55] Fusō sailed to Tarakan Island off Borneo to refuel in early July before returning to Japan, escaping an attack by the submarine USS Pomfret.

They departed Kure on 23 September for Lingga Island, carrying the Army's 25th Independent Mixed Regiment, and escaped an attack by the submarine USS Plaice the next day.

They arrived on 4 October, then transferred to Brunei to offload their troops and refuel in preparation for Operation Shō-Gō, the attempt to destroy the American fleet conducting the invasion of Leyte.

[59] Nishimura radioed Admiral Soemu Toyoda at 20:13: "It is my plan to charge into Leyte Gulf to [reach] a point off Dulag at 04:00 hours on the 25th.